revocation: split up methods to get current pre-image and hash
revocation: split up methods to get current pre-image and hash

AndrewSamokhvalov/lnd,BitfuryLightning/lnd,aakselrod/lnd,bryanvu/lnd,ddustin/lnd,aakselrod/lnd,BitfuryLightning/lnd,LightningNetwork/lnd,LightningNetwork/lnd,bryanvu/lnd,AndrewSamokhvalov/lnd,ddustin/lnd